Flare Stack

ABSTRACT

In one aspect there is provided a gas flare comprising a hollow cylindrical member having a bottom end, a top end, a discharge end at said top end, and defining an interior volume having a mixing region. The gas flare further comprises a gas inlet to receive waste fluids, an air inlet to receive and direct air into the interior volume, and an internal riser having an outlet. The mixing region is located above the air inlet and below the discharge end. The internal riser fluidly and sealably connects to the gas inlet and directs all waste fluids from the gas inlet, out through the outlet, into the mixing region.

CROSS REFERENCE TO RELATED APPLICATION

This application is a non-provisional application which claims priorityto, and benefit of, U.S. Provisional Patent Application Ser. No.62/774,109 filed Nov. 30, 2018 and entitled, “IMPROVED FLARE STACK”, theentirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The field of present invention relates generally to flares and flaresystems used at oil and gas well sites and, more particularly, to animproved flare stack.

BACKGROUND OF THE INVENTION

The background information discussed below is presented to betterillustrate the novelty and usefulness of the present invention. Thisbackground information is not admitted prior art.

A variety of apparatus for flaring combustible waste fluid streams havebeen developed and used in the past. Such apparatus are often referredto as flares, gas flares, or flare stacks. Flares dispose of wastefluids, such as hydrocarbon gasses, in an environmentally compliantmanner through the use of combustion. Flares are commonly located atproduction, refining and other processing plants. They are a criticalcomponent of a system design intended for safely disposing ofcombustible wastes or other combustible streams, such as hydrocarbonsfrom pressure-relieving and vapour-depressurizing systems.

Referring to FIG. 1, a flare stack is generally a hollow cylindricalmember that may include a flare section having a discharge end which,during operation, is positioned some distance or height above the groundto direct the combustion products and combustion gasses high up into theatmosphere, so that they may be more readily dissipated into ambient airby prevailing air currents. The flare may be connected to stack by meansof a hinged or flanged connection, so as to further increase the flare'sheight above the ground during operations. Flare stacks may be hundredsof feet in height, and a hinged connection facilitates transport of aflare stack on a truck, trailer or the like, such as when it needs to betransported in a collapsed state between job sites.

Continuing to refer to FIG. 1, the flare and stack (together referred toas a flare stack) are typically hollow tubular members constructed ofmetal and are substantially air/gas tight so as to direct thehydrocarbon gasses from a gas inlet (which is generally locatedsubstantially adjacent the bottom of the flare stack), through theflare's interior volume, and then out of an outlet at the discharge end(which is generally located substantially adjacent the top of the flarestack). A drain and drain valve may be provided near the bottom of theflare stack to facilitated draining of condensate and other liquids thatmay build up in the flare's interior volume over time.

Unfortunately, the efficient flaring of methane or other flammable wastegasses in oil and gas field operations has been a problem for manydecades. Gas compositions can change greatly, including from havinghydrogen sulfide (H₂S) in the gas stream to containing varying degreesof light ends. Light ends become more dominant in high temperature flowbacks. Research has been done to determine the combustion efficiency ofmethane gas. But it is very difficult to simulate actual flow conditionson a well site. Conditions of the flow parameter will also change as thewell cleans up from different operations, such as fracturing, acidizingor clean out operations. Even as the well goes from shut in to flowingconditions, the gas properties will change to some degree. Burnefficiencies will also change with the gas rate being flared. Researchindicates that higher gas rates based on flare stack diameter will burnat a higher degree of destruction than lower rates. Research alsoindicates that wind conditions affect the destruction quality of theburn.

Attempts have been made to resolve the flaring issues. Most involve tipdesign, or injection of gas or air. Injection of air or gas requires apumping device of some sort and would, in order to be efficient, have tovary injection rates to follow varying gas flow rates. If methane werethe required injection source, then a pipeline or production facilitywould have to be relatively close by and piping would be required alongwith process equipment to regulate the required flow, as flow parameterschanged.

Most flares are designed with a shroud or can at the top of the flarestack around the discharge end; see FIG. 1. The purpose of the shroud isto, in some cases, allow for an air draw from the bottom of the shroudand also to partially protect the flame during windy conditions. In thecases where the air draw is designed into the stack via a shroud, suchdrawn air is usually not in sufficient volumes to ensure a good burn.Moreover, the intake air is typically concentrated to the outer portion(or periphery) of the flare's interior volume and waste gasses beingburned. This prevents a good portion of the inner gas flow not to havethe adequate air/gas mixture to ensure total combustion. Such incompletecombustion or burning of the gases then unduly contaminates the ambientatmosphere, increases smoke emissions, and reduces flame luminosity.Therefore, what is needed is an improved flare stack that does notsuffer from these disadvantages and inefficiencies.

SUMMARY OF THE INVENTION

In one aspect there is provided a gas flare comprising a hollowcylindrical member having a bottom end, a top end, a discharge end atsaid top end, and defining an interior volume having a mixing region.The gas flare further comprises a gas inlet to receive waste fluids, anair inlet to receive and direct air into the interior volume, and aninternal riser having an outlet. The mixing region is located above theair inlet and below the discharge end. The internal riser fluidly andsealably connects to the gas inlet and directs all waste fluids from thegas inlet, out through the outlet, into the mixing region.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings, several aspects of the present invention areillustrated by way of example, and not by way of limitation, in detailin the figures, wherein:

FIG. 1 is a diagrammatic, sectional, side elevation view of a PRIOR ARTflare stack;

FIG. 2 is a diagrammatic, sectional, side elevation view of oneembodiment of a flare stack of the present invention; and

FIGS. 3a-3c are perspective, side views of the flare stack of FIG. 2alongside a prior art flare stack, both shown in operation and bothhaving a flame plume.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of preferred embodiments by way of exampleonly and without limitation to the combination of features necessary forcarrying the invention into effect. Reference is to be had to theFigures in which identical reference numbers identify similarcomponents. The drawing figures are not necessarily to scale and certainfeatures are shown in schematic or diagrammatic form in the interest ofclarity and conciseness.

A first embodiment of the flare stack 10 of the present invention isshown in FIG. 2. The flare stack 10 is preferably a hollow cylindricalmember having a bottom end 10 b, a top end 10 t and defining an interiorvolume 10 v. The flare stack 10 may include a flare section 12 having adischarge end 18 at the top end 10 t which, during operation, ispositioned some distance or height above the ground R to direct thecombustion products and combustion gasses high up into the atmosphere.The flare 12 is preferably mounted on top of a stack section 14 by meansof a hinged or flanged connection 16, so as to further increase theflare's height above the ground R during flaring operations. A gas inlet19, to receive waste fluids and gases G to be combusted, is preferablyprovided at the bottom end 10 b. A conventional shroud 20 is preferablyprovided at the discharge end 18. Air A may travel through the shroud 20via inlets 21 at the shroud's bottom 20 b in a conventional manner. Aconventional drain with drain valve 22 is preferably provided at thebottom end 10 b.

The flare stack 10 further comprises an internal riser 30 having anoutlet 32. The riser 30 is a tubular member which fluidly and sealablyconnects to the gas inlet 19 so as to direct all waste gas G, thatenters the flare stack 10 via inlet 19, out through the outlet 32 andinto a mixing region 10 m within the interior volume 10 v. The outlet 32may be provided with a nozzle 32 n to adjust, e.g. raise or lower, therate of waste gas G exiting out of it. The riser 30 is of a smallerdiameter than the interior diameter of the flare stack 10. For example,in an embodiment where the flare stack 10 has a six (6) inch diameter, asuitable diameter for the riser 30 and outlet 32 is three (3) inches formost common flaring operations. Further, in such an embodiment, a nozzle32 n to reduce the outlet down to two (2) inches, or increase it to four(4) inches may be provided to adjust the flow of gas G out the outlet 32as may be desired and in relation to particular well and gas flowconditions. The outlet 32 may be provided with a threaded end (not show)and the nozzle 32 n may also be provided with a matching threaded end(not shown) so that the nozzle 32 n may be easily installed on and/orremoved from the outlet 32.

The riser 30 is preferably mounted substantially centrally andco-axially to the flare stack 10 within the interior volume 10 v, so asto create an annulus 40 between the riser 30 and the flare stack'sinterior wall 10 w. The riser 30 may be supported and centralized bymeans of mounting brackets 35 or the like. In an alternate embodiment(not shown), the riser 30 may be mounted peripherally against one sideof the flare's interior wall 10 w. In such a case, the region 40 betweenthe riser 30 and the flare stack's interior wall 10 w will not be anannulus, but have some other cross-sectional shape. The riser 30 may beconstructed of metal pipe or the like.

The riser's outlet 32 is preferably located some distance from theflare's bottom end 10 b. For example, in an embodiment where the flarestack 10 is sixty (60) feet tall, and the connection 16 is at thehalf-way point, at thirty (30) feet, the riser 30 preferably extends upalong the interior volume 10 v so as to place the riser's outlet 32 justbelow the connection 16. As such, the gas G that conventionally wouldenter the interior volume 10 v a few inches above the bottom end 10 b(via the inlet 19) is now directed to enter the interior volume 10 v atapproximately the half-way point up the flare stack 10 (i.e. almostthirty feet up above the bottom end 10 b, in a sixty feet tall flarestack 10). Advantageously, by positioning the outlet 32 just below theconnection 16, the top part of the flare stack 10 (i.e. flare 12) may bedisconnected, and pivoted away, from the bottom part (i.e. the stack 14)so as to then provide an operator with easy access to the outlet 32 toinstall or change any nozzle 32 n.

The flare stack 10 further comprises an air inlet 50 to direct air Ainto the annulus 40 (or similar region between the riser 30 and interiorwall 10 w). Air A may be atmospheric air from just outside the exteriorof the flare stack 10, or it may be air from another source. Preferably,the inlet 50 further comprises a valve 52 to allow an operator tocontrol if/when air A can enter the annulus 40. In an embodiment of theflare stack 10 where the stack is a six inch diameter, sixty feet tallcylindrical flare stack, where the gas inlet 19 and riser have adiameter of three inches, then the air inlet 50 preferably has a fourinch diameter.

During operations when the valve 52 is opened and air A is allowed toenter the annulus 40, then such air A will typically fill the annulus 40and rise up towards the riser's outlet 32. If gas G is moving throughthe inlet 19, up the riser 30, out the outlet 32 and expanding into theinterior volume 10 v, then a venturi effect is created drawing up moreair A into the annulus 40 via the air inlet 50. In an embodiment wherethe flare stack has a 6 inch diameter, a 60 feet total height, whereinthe riser 30 has a 3 inch diameter and the outlet 32 is positioned justbelow the connector 16, the inventor(s) expect that during typical oilfield flaring operations the venturi effect will generate approximately5 PSI of vacuum; which the inventor(s) calculate out to create in excessof 1 mmcf/d of additional air A draw into the annulus 40. Preferably avacuum gauge 45 is provided to measure any such vacuum that is createdin the annulus 40.

Valve 52 can also be utilized during operations, e.g. to be closed priorto shut in of an oil- or gas-well being flared, to reduce the amount ofoxygen within the interior volume 10 v, and thereby prevent or limit anyflame or internal combustion within the interior volume 10 v. Duringnormal operations, however, the flare stack 10 and nozzle 32 aredesigned to ensure enough gas G velocity to create the desired venturieffect and to prevent an internal burn. Also note that when the gas Gflow rate dies down (e.g. due to a shut in situation) the venturi effectlessens and the air A draw through inlet 50 shuts down as well. In asituation where a flare stack 10 is left unattended, it could be fittedwith an electronic air inlet valve 52 set to open and shut atpredetermine vacuum values (e.g. as measured by vacuum gage 45). Thiswill enhance the safety aspect of the flare stack 10 in the event of awell shut in when unattended.

As can be seen and during normal operations, when gas G moves up theflare stack 10 and out the outlet 32, and as air A is drawn up into theannulus 40, both the gas G and air A will thoroughly mix in a mixingregion 10 m that is situated between the outlet 32 and the discharge end18. While a mixing region 10 m of only a few inches in height (e.g. 3inches along the flare stack's height, below the discharge end 18) willallow for gas G and air A to mix, preferably the mixing region 10 mextends from just below the connector 16 all the way to the dischargeend 18, thereby allowing for a very thorough and complete mixing ofwaste gas G with air A (note that waste gas G is illustrated in thefigures by solid arrows, while air A is illustrated by hatched arrows).Preferably, a sampling port 47 is provided to allow an operator towithdraw or sample some of the gas G and air A mixture in the annulus40.

As will now be appreciated, this mixture of gas G and air A will burnmuch more efficiently once ignited at the discharge end 18 as comparedto a conventional flare stack where, at best, only some air isintroduced only at the periphery of the gas flow by a conventionalshroud 20. Advantageously, this mixture of gas G and air A is created bythe flare stack 10 without the need for additional mechanical blowers.Note that, while referring to “bottom” and “top” ends of the flarestack, the embodiments of the invention also contemplate horizontalflare stacks, wherein these terms will then refer to inlet and dischargeends respectively.

Preferably, the flare stack 10 further comprises a drain with a drainvalve 22 at the bottom end. More preferably, and in a vertical flareembodiment, the drain 22 is located below the air inlet 50 so as tocreate a sump region 60 to receive any condensates or fluids that mightcondense within the interior volume 10 v and travel down the annulus 40.For example, if the flare stack 10 of the present invention is use on a“hot” well, where the gas G has a higher temperature coming out of thewell than the ambient air, the inventors have observed that the air Amoving up the annulus 40 has a chilling effect to that gas G (withinriser 30) and will cause an increase in condensate forming within theinterior volume 10 v once the gas G enters the mixing region 10 m. Thiscondensate will then fall and drain into sump region 60 at a higher rateas compared to conventional flare stacks. Advantageously, suchcondensate falling and draining into the sump region 60 will reduce theamount of black smoke that will otherwise be emitted by a conventionalflare stack (because less condensate is being burned). Preferably, andin cases where a significant amount of condensates and fluids arecollected during flaring operations, the bottom end 10 b of the flarestack 10 may be expanded or enlarged to provide an increased sump region60. Likewise, the air inlet 50 may be positioned a higher up the stack14, up above the drain 22, to create a greater sump region 60 and/or toreduce the chilling effect that such air A has on the riser 30. Morepreferably, a vacuum system (not shown) is connected to the drain 22 tofacilitate emptying the sump region 60 of such condensate and fluids(e.g. during times when the flare stack is non-operational, or in such amanner so as not to interfere with any venturi effect that is created atthe outlet 32).

Now with reference to FIGS. 3a-3c , the inventors have observed thatwhen using the flare stack 10 of the present embodiment along-side asimilarly sized conventional flare stack 70, both stacks 10, 70operating with the same flow rate of waste gas, the flare stack 10 ofthe present embodiment results in a bright (higher luminosity) flameplume 80 with little, if any, black smoke 82. This indicates that theflare stack 10 of the present embodiment provides a more efficient burnof the waste gas G than conventional flare stacks 70.

Those of ordinary skill in the art will appreciate that variousmodifications to the invention as described herein will be possiblewithout falling outside the scope of the invention. In the claims, theword “comprising” is used in its inclusive sense and does not excludeother elements being present. The indefinite article “a” before a claimfeature does not exclude more than one of the features being present.

1. A gas flare comprising: a hollow cylindrical member having a bottomend, a top end, a discharge end at said top end, and defining aninterior volume having a mixing region; a gas inlet to receive wastefluids; an air inlet to receive and direct air into the interior volume;and an internal riser having an outlet; wherein said mixing region isabove the air inlet and below the discharge end; wherein the internalriser fluidly and sealably connects to the gas inlet and directs allwaste fluids from the gas inlet, out through the outlet, into the mixingregion.
 2. The gas flare of claim 1 wherein the hollow cylindricalmember further comprises: a flare section; and a stack section.
 3. Thegas flare of claim 2 wherein the flare section is mountable on top ofthe stack section by means of a connection.
 4. The gas flare of claim 3wherein the connection is a hinged connection.
 5. The gas flare of claim3 wherein the connection is a flanged connection.
 6. The gas flare ofclaim 1 wherein the internal riser is mounted substantially centrallyand coaxially within the interior volume, thereby defining an annuluswithin said interior volume.
 7. The gas flare of claim 6 wherein the airinlet directs air into the annulus.
 8. The gas flare of claim 7 furthercomprising an air inlet valve to control the amount of air entering inthe annulus via the air inlet.
 9. The gas flare of claim 3 wherein theinternal riser extends up along the interior volume so as to positionthe riser's outlet just below the connection.
 10. The gas flare of claim9 wherein the mixing region extends the outlet to the discharge end. 11.The gas flare of claim 1 further comprising a drain positionedsubstantially at the bottom end.
 12. The gas flare of claim 11 furthercomprising a drain valve to open or close said drain.
 13. The gas flareof claim 12 wherein the drain is located below the air inlet, therebydefining a sump region.
 14. A gas flare comprising: a hollow cylindricalmember having an inlet end, a discharge end, and defining an interiorvolume having a mixing region; a gas inlet to receive waste fluids; anair inlet to receive and direct air into the interior volume; and antubular member having an outlet; wherein said mixing region is above theair inlet and below the discharge end; wherein the tubular memberfluidly and sealably connects to the gas inlet and directs all wastefluids from the gas inlet, out through the outlet, into the mixingregion.
 15. The gas flare of claim 14 wherein the tubular member ismounted substantially centrally and coaxially within the interiorvolume, thereby defining an annulus within said interior volume.
 16. Thegas flare of claim 15 wherein the air inlet directs air into theannulus.
 17. The gas flare of claim 16 further comprising an air inletvalve to control the amount of air entering in the annulus via the airinlet.